Four rhesus monkeys were implanted with chronic indwelling intravenous cannulas and allowed to self-inject nicotine. After 74, 126, and 147 self-administration sessions respectively in three of the monkeys, nicotine self injection increased to above saline levels. (The fourth monkey has had over 200 nicotine self-injection sessions without significant self-injection of the drug.) During the acquisition period, nicotine doses of 2-150 micrograms/kg/inj. were tried, using fixed-ratio schedules (in which a fixed number of responses on a lever is required before an injection is delivered), second-order schedules (in which only the first response after 60 sec produced a drug injection), and a schedule in which the duration of the lever-press response determined the injection dose. A series of programmed noncontingent injections (every 10 mins throughout the 126-min session) was also tried in three of the monkeys. Increases in nicotine self-injection were seen only after employing the second-order schedule and after decreasing the injection duration to 1 second. Programmed injections either had no effect or resulted in a temporary increase in nicotine self-injection followed by a decline to saline levels within 4-6 daily sessions. A relationship between unit dose and the number of responses, number of injections, and drug intake per session is being found, but the overall shape of the functions cannot be established at this time. Drug intake per session varies from 210 micrograms/kg (base) at an injection dose of 15 micrograms/kg, to 5,040 micrograms/kg at an injection dose of 180 micrograms/kg. Response rate and drug intake is highest at the beginning of the session and the amount of the drug taken in this period is related to the injection dose size by an inverted 'U' shaped function, with a peak intake of about 1,500 micrograms/kg at 90 micrograms/kg/inj.